The present invention relates to process control, and in particular to the monitoring of parameters representative of a process.
Typical industrial process control involves the use of a control system to monitor many process parameters. In the control of petrochemical, power, pharmaceutical and many other types of plants requiring process control, there can be several hundred parameters representative of flow, temperature, pressure and level, as well as many other parameters which are measured by sensors coupled to a computer based control system. The computer system may comprise a single processor, or as common in distributed process control, several processors which monitor the measured parameters, and provide process control signals to valves, pumps, motors, heaters and other devices which control the process being monitored. In addition, many predefined parameter limits are programmed into the computer system. When these limited are exceeded, alarms may be communicated to users called operators who monitor the operation of the process.
When setting up the computer system to control the process, process engineers configure the computer system with control programs to control the process as desired. Process engineers also set the alarm limits based on their detailed knowledge of the process to ensure that the process operates within safe and/or efficient limits. These alarm limits are not normally modifiable by an operator because they are usually set to be indicative of an unsafe condition. When an abnormal condition or situation in the process occurs such as during startup, or an overflow condition, there may be a long list of alarms that are currently being communicated to the operator. Alarms may be communicated by sound, blinking representations of parameters on one or more displays, messages or other forms of communication. The alarms may or may not be important depending on the condition. There are also computer screens of other information that are displayed, such as schematics/groups of process flow, overviews, and trends in addition to various forms of alarms. The operator may be busy trying to control the process, and be interested in one or more parameters that are not near a limit. The operator may be waiting to perform an action when one or more parameters reach values well within alarm limits. With potentially hundreds of alarms being communicated and hundreds of screens of information, it is difficult for the operator to monitor such parameters to know when to take another action to bring the process back under control or to follow a normal procedure.
Basic human nature also makes it difficult for a person to continuously track one or more parameters. In observed cases, operators have been known to leave doors open on strip chart devices to remind them that the process variables represented on the charts needed closer attention. In extreme cases, operators have been known to defeat security mechanisms and actually change the predefined alarm limits to monitor a process variable. This is potentially dangerous, as the predefined alarm limits are designed to provide warning for unsafe operation of the process which could lead to catastrophic results. Operators may neglect to tell the next shift about the change, or may themselves forget the prior limit or forget to set it back.
A user interface provides the operator of a process control system the ability to set user-initiated alarms on selected parameters representative of a process being controlled, independent of predetermined alarm limits. The interface allows the operator to identify parameters to monitor, when to monitor the parameters, when to trigger alarms, and allows the operator to determine how to be notified that a user-initiated alarm has been triggered.
In one embodiment, the operator interface comprises a computer program running on top of a window based operating system that operates on a user station attached to many process modules through various networks. The process modules monitor all parameters in real time and compare them to predetermined alarm limits which are set by engineers who initially configured the process control system. The operator interface permits the operators to select multiple parameters to monitor and to set the user-initiated alarm limits, as well as indicate the type of notification to be given when such a limit is triggered. Values of the parameter are obtained from the process module coupled to the device generating the parameter. The values are then compared to the selected alarm limits by the operator interface program running on the user station.
In a further embodiment, the process module performs the comparison for both the predefined limits and the operator-defined limits and generates predefined alarms for the predefined limits being exceeded, and generates user-initiated alarms for the operator selected limits being exceeded.
In a further embodiment, a list of parameters is provided in a graphical user interface format allowing the operator to point to and select parameters using any of a number of well known pointing devices such as a mouse. When a parameter is selected, a panel is provided showing selected information about the parameter, such as what it represents, and current fixed alarm limits if any. Further portions of the panel provide space for the operator to select desired operator limits and associated notification methods. Time limits for such notification may also be specified.
Parameters may also be selected by clicking on an icon representative of a sensor or device such as a valve in a schematic display. Control points or parameters to select are then displayed based on which are relevant to the valve.
In an alternative embodiment, a menu driven interface is provided such that the selection of parameters and operator specified alarm limits is performed by use of a standard keyboard.
Once the operator selects a parameter to be modified, it sends a message indicating the device, referred to as a point, to be monitored along with a time interval frequency indication ranging from 1 to 60 minutes. The process module monitoring the device generating the parameter receives the message and then proceeds to monitor the device at specified frequency. It provides the parameter value at each time interval, or only upon change if so specified, along with a point identifier in a broadcast message which the user station will pick up and perform alarm limit comparisons, as well as generate appropriate alarms. In the alternative embodiment where the process module does the monitoring, it merely sends an alarm as specified by the user. In yet a further embodiment, a network interface module which couples the user station with multiple process modules performs the user-initiated alarm limit calculations.
In yet further embodiments, the operator may take actions based on the alarm, such as turning off or on of selected valves based on a monitored parameter reaching an operator specified limit. An operator may operate valves and motors manually or through normal process control interface software. Modes of control may also be changed, such as from manual to automatic or cascade, as well as modification to various PID control types.
The present invention provides the operator with an efficient method of monitoring selected parameters and being alerted when they reach desired values. It is intended to avoid inappropriate use of the alarm system and offload the operator from having to remember to monitor parameters, and what levels to trigger key events. This is done on a temporary basis as controlled by the operator. In addition, when operator work shifts change, it is much easier to bring the new operator up to speed simply by reviewing all operator initiated alarms.